My Acer XR341CK has a feature to always display refresh rate in a corner.
Refresh rate syncs with FPS reported by game up the the point you pick a hero, but while in a match, it is stuck at 75Hz, while FPS reported by the game fluctuates between 72-75. My frame cap is set to 75, since at first i thought it was because of the refresh rate+10 cap.
Graphics card is XFX RX480 LED V1 (not Black Edition), Freesync is enabled in AMD software and the status light of the monitor changes when game is open.
Same/similar thing happens in HOTS - while in match, game reports 60-70fps but refresh barely fluctuates from 75. Out of fame it syncs fine.
FreeSync requires the game to run in exclusive fullscreen mode to function, you can test if it is working by using the FreeSync Windmill Demo.